Two non-invasive radiation techniques have been developed to measure lead in bone; K-shell and L-shell X-Ray Fluorescence (XRF). Both provide quantitative data on bone-lead content. The two techniques have not undergone direct comparison. We hypothesize that the two technologies will provide different and complementary information on bone-lead burden, in that L XRF gives data on lead in superficial, mainly subperiosteal bone, whereas K XRF provides data on deep or whole bone-lead content. We hypothesize further that superficial bone-lead is more closely correlated with chelatable lead, the standard clinical indicator of lead accumulation, but that deep bone-lead is the better marker of cumulative absorption and hence of chronic toxicity. To test these hypotheses, we propose to construct a state-of-the-art L- shell XRF instrument and then conduct a study to compare and contrast the K and L XRF techniques. This study will be undertaken within the Heavy Metals core of the Mount Sinai Environmental Health Sciences Center. A polarized L XRF system will measurement system. Operating characteristic and limitations will be defined: precision; detection limit; than lead (particularly arsenic); and effective (radiation) dose. To determine whether the K and L technologies provide data on lead in two distinct compartments within the body lead burden, analyses will be conducted by intact was well as with the soft-tissue remove. Chemical analyses by atomic absorption spectrophotometry of deep and superficial bone samples obtained from the same sites in the same legs will provide additional experimental validation of the XRF techniques. To determine whether the two technologies are measuring compartments containing lead of differential accessibility, and an examination of the effects of chelation therapy will be performed. Both K and L XRF will be used to measure lead content of bone both before and after therapeutic chelation in a population of sixty construction workers occupationally exposed to lead. Data from this study will extend current understanding of the radiation technologies used to measure bone-lead content and will increase knowledge of the toxicokinetics of lead in bone.